Leftover Salmon returns to recording after an eight-year absence with Aquatic Hitchhiker, a song collection that revives the group’s “polyethnic cajun slamgrass” sound while adding a few new twists. New recruit Andy Thorn finds common ground with the eclectic instincts of band co-founders Vince Herman and Drew Emmitt as they offer up a set brimming with regional Americana flavors and deft instrumental embellishments. Leftover Salmon made its rep two decades ago by straddling the bluegrass and jam-band realms; its latest incarnation still crosses genre boundaries without restraint. Brisk ‘grassy rambles like “Keep Driving” and “Kentucky Skies” are featured alongside Cajun waltzes like “Bayou Town” and calypso-accented numbers like “Liza.” The prevailing mood is friendly and relaxed, whether the guys are catching a buzz under country skies (“Sing up the Moon”), taking a romantic getaway down South (“Gulf of Mexico”), or just going where their feet lead them (“Walking Shoes”). Aquatic Hitchhiker’s instrumental title tune offers the sort of subtle textures and rousing dynamics that have become the quintet’s trademarks.